the
Natural History Museum, New York, has furnished information concerning
two other fine crystals placed in the Morgan collection. One of these
is 9 inches high, 5 inches wide, and about three-fourths of an inch
thick. It shows a fine deep suffused lilac coloration when viewed
parallel to the vertical axis or length. The other crystal is 7 inches
high, 5 inches wide, and three-fourths of an inch thick. Both arc of
gem quality and are free of all matrix and associations. They are
strongly striated as usual, but have perfect terminations.
TOPAZ.
TEXAS.
The
following notes on the occurrence of topaz in Mason County, Tex., have
been abstracted in great part from a description by II. Conrad Meyer.1
Topaz has been found at two places near Streeter and near Katemcy,
respectively. Streeter is about 8 miles due west and Katemcy about 12
miles north of Mason, the county seat. This discovery of topaz was
made in 1904 by the late R. L. Parker, of Streeter. Mr. Parker was
attracted by the unusual weight of a supposed quartz crystal he had
found in the bed of a stream on the land of Sam Await, near Streeter.
He submitted it to a mineralogist, who pronounced it topaz. A careful
search revealed the original matrix of the topaz, but the first work
was confined chiefly to ' 'dry washing" of the alluvial deposits. The
topaz thus obtained consisted of waterworn crystals, with
frosty-appearing surfaces. These were found to contain clear, limpid
interiors when broken. Regular development of the topaz vein was not
undertaken until 1908. Only a limited amount of work has been done on
any of the deposits since 1910. In all a dozen or more prospect holes
have been made at this locality.
Meyer refers to the report on the rare-earth minerals of Llano County, by F. L. Hess,2
for a general description of the geology of the region. Hess speaks of
the Llano region as an island of pre-Cambrian rocks intruded by
plutonics and surrounded by an irregular zone of Cambrian and other
Paleozoic rocks. The principal plutonic rocks are granites, which
present several phases. An important variety, and one which Meyer
mentions as the country rock at the topaz localities, is a rather
coarse-grained red granite. The general geology of the Llano region,
including a more complete description of this granite, has been given
by Sidney Paige.3
The
topaz occurs in pegmatite, but with different associations at the two
localities. At the locality near Streeter the crystals are found in
vugs partly filled with clay and associated with microcline feldspar,
biotite, tourmaline, smoky quartz, and albite. The microcline is
flesh-colored and occurs in large crystals. Smoky quartz, in many
places intergrown with topaz, and biotite are quite abundant. The
albite is found in fan-shaped laminated aggregates and is the
clevelandite variety. Black tourmaline is sparingly present in small
needle-like crystals. Some 200 pounds of good topaz crystals have been
obtained. Besides the clear, colorless crystals, a small number of
beautiful light-blue crystals, rivaling those of Siberia, have been
1 Topaz and stream tin in Mason County, Tex.: Eng. and Min. Jour., Mar. 8,1913, pp. 511-512.
• Bull. U. S. Geol. Survey No. 340,1908, pp. 286-294.
' Llano-Burnet [olio (No. 183), Geol. Atlas U. S., U. S. Geol. Survey, 1912.
